The present invention relates to refrigerant compositions, particularly for use as replacements in refrigeration equipment currently employing, or designed to employ, the refrigerants R12 and R22.
Refrigerant R12 (CCl2F2) has been a commonly used refrigerant especially in domestic refrigerators. However, R12 contains chlorine atoms and has been implicated in environmental damage to the ozone layer. As a result efforts have been made to replace R12 with a refrigerant formulation which does not involve the use of refrigerants such as R12 which contain chlorine atoms. Similar comments apply to R22 which is used principally for airconditioning systems.
Among alternatives, particular attention has been directed at R134a (C2H2F4; 1,1,1,2-tetrafluoroethane) along with pentafluoroethane (R125) (b.pt. xe2x88x9248.6xc2x0 C.). Commercial formulations of these two refrigerants involve the use of a hydrocarbon, namely propane, propylene or isobutane. While these refrigerant formulations are generally effective as replacements for R12 and R22, nevertheless it has been found that their use is not entirely satisfactory.
Difficulty has arisen with the flammability of the fractionated composition, that is to say the vapour above the liquid composition possesses flammability problems. As a result these commercial formulations can produce flammable compositions under some leak scenario conditions. The flammability of these refrigerant compositions resides in their hydrocarbon content. One of the purposes of incorporating the hydrocarbon is so that the formulation is compatible with the lubricants ordinarily used in R12 and R22 refrigeration equipment. The specific hydrocarbons have been selected because they possess the correct boiling point in relation to that of the fluorocarbon.
It has now been found, surprisingly, according to the present invention, that if a hydrocarbon with at least 4 carbon atoms other than methyl propane (isobutane) is used instead of those previously advocated the flammability of the fractionated composition is greatly reduced. This result is very surprising as n-butane, for example, has a significantly higher boiling point (xe2x88x920.5xc2x0 C.) than, say, isobutane (xe2x88x9211.7xc2x0 C.) and is accordingly less volatile. Indeed, the US NIST (National Institute of Standards and Technology) computer programs REFPREP and REFLEAK have predicted that a particularly preferred such n-butane-containing formulation would be flammable when it has been found not to be. Further, although there can be a considerable boiling point range between the lowest boiling point component and the hydrocarbon of the composition the temperature glide of the blend is relatively small. In a particular embodiment, although the boiling point range is 36.2xc2x0 C., the temperature glide is only 3.9K at the boiling point of xe2x88x9234.6xc2x0 C. at one atmosphere pressure. It is further surprising that such a formulation has a reduced flammability because n-butane, for example, has a larger range of flammability limits as compared with isobutane. Thus n-butane has a flammability range from 1.5 to 10.1% v/v whereas for isobutane it is only 1.7 to 9.7% v/v.
According to the present invention there is provided a refrigerant composition which comprises:
(a) R125, R218 (octafluoropropane; b.pt. xe2x88x9236.7xc2x0 C.), trifluoromethoxy difluoromethane (b.pt. xe2x88x9234.6xc2x0 C.) or hexafluoro-cyclopropane (b.pt. xe2x88x9231.5xc2x0 C.), or a mixture of two or more thereof, in an amount from 5 to 60% by weight based on the weight of the composition
(b) R125, R134a, R134 (1,1,2,2-tetrafluoroethane), 1,1-difluoroethane (R152a; b.pt. xe2x88x9224.7xc2x0 C. ), trifluoromethoxypentafluoroethane (b.pt. xe2x88x9223.3xc2x0 C. ), 1,1,2,3,3,3-heptafluoropropane (R227ea; b.pt. xe2x88x9218.3xc2x0 C.) or 1,1,1,2,2,3,3-heptafluoropropane (R227ca; b.pt. xe2x88x9216.3xc2x0 C.), or a mixture of two or more thereof, in an amount from 30 to 94% by weight based on the weight of the composition and
(c) an unsubstituted hydrocarbon of the formula CnHm in which n is at least 4 and m is at least 2nxe2x88x922, other than methyl propane, in an amount from 1 to 10% by weight based on the weight of the composition.
The present invention also provides a process for producing refrigeration which comprises condensing a composition of the present invention and thereafter evaporating the composition in the vicinity of a body to, be cooled. The invention also provides a refrigeration apparatus containing, as refrigerant, a composition of the present invention.
Component (c) will be present in an amount from 1 to 10%, especially 1 to 8%, preferably 2 to 6% and more preferably 2 to 5%, and in particular 3 to 4%, most preferably about 3.5%, by weight of the composition.
It will be appreciated that component (a) and component (b) can both be R125. In this situation the composition can, therefore, be binary and the amount of R125 will be from 90 to 99% by weight. In all other situations, the composition will be at least ternary.
Among the preferred compositions of the present invention are those which contain one or more of R125, R134a and R218. Thus component (a) preferably comprises R125 and/or R218 while component (b) preferably comprises R125 and/or R134a.
The presence of R218 (b.pt xe2x88x9236.7xc2x0 C.) is particularly useful where the only other fluorocarbon is R134a. In such circumstances R218 is particularly present in an amount from 5 to 20% by weight, especially 5 to 15%, and more preferably 7 to 12% by weight of the composition.
Component (a) is present in an amount from 5 to 60% by weight, generally 5 to 50% by weight. If R125 does not form part of component (a) then the amount will typically be from 5 to 20%, especially 5 to 15% and preferably 7 to 12%, by weight. It will be appreciated that if the composition contains R125, the concentration of R125 can be split between components (a) and (b).
The concentration of component (b) is from 30 to 94% by weight, generally 50 to 90% and especially 75 to 90%, by weight.
Typically hydrocarbons which can be employed as component (c), and which may be saturated or unsaturated, possess 4 or 5 carbon atoms and include methylenecyclopropane, 1-butene, cis and trans-2-butene, butane, cyclobutane, cyclopentene, cyclopentane, 2-methyl-1-butene, 2-methyl-2-butene, 3-methyl-1-butene, 1-pentene, cis and trans-2-pentene, 2-methylbutane, pentane and mixtures of two or more thereof. The use of n-butane (R600) is particularly preferred.
Specific formulations which have been found to be effective are as follows:
It has also been found that certain compositions with specific amounts of n-butane as component (c) have particularly advantageous properties. According to the present invention, there is also provided a refrigerant composition which comprises (generally in the liquid phase):
(a) pentafluoroethane, octafluoropropane, trifluoromethoxydifluoromethane or hexafluoro-cyclopropane, or a mixture of two or more thereof, in an amount of at least about 35% based on the weight of the composition,
(b) 1,1,1,2- or 1,1,2,2-tetrafluoroethane, 1,1-difluoroethane, trifluoromethoxypentafluoroethane, 1,1,1,2,3,3-heptafluoropropane or a mixture of two or more thereof, in an amount of at least about 30% by weight based on the weight of the composition and
(c) n-butane, in an amount from about 2.3 to about 4% by weight based on the weight of the composition.
Component (a) is present in an amount of at least 35% by weight based on the weight of the composition. In practice, the concentration will generally be at least 40% by weight although a general range is 35 to 65% by weight. A preferred range is 40 to 55% by weight, especially 45 to 52% by weight. Preferably, component (a) is R125.
Component (b) is present in the composition in an amount of at least 30% by weight based on the weight of the composition. Typically, the component is present in an amount from 35% to 60% by weight, preferably 45 to 60% and especially 47.5 to 55% by weight. Component (b) is preferably R134a.
Component (c) is n-butane. It has been found that the best results are obtained using about 3.5% by weight based on the weight of the composition. Generally amounts greater than this can give rise to flammability problems. Generally the performance of the composition deteriorates as the concentration of butane is decreased down to 2.3% by weight. Similarly, for a given butane content, the performance characteristics of the composition deteriorate as the concentration of R125 is increased.
The presence of at least one further component in the compositions is not excluded. Thus although, typically, the composition will comprise the three essential components, a fourth component, at least, can also be present. Typical further components include hydrocarbons such as propane and isobutane as well as other fluorocarbons. In general, the maximum concentration of these other ingredients does not exceed 30% by weight, typically not exceeding 20%, preferably not exceeding 10% and especially not exceeding 5% by weight, based on the sum of the weights of components (a), (b) and (c). Further it is desirable that the maximum hydrocarbon content in the composition does not exceed 4% by weight. Desirably the n-butane represents at least 70%, preferably at least 80% and more preferably at 90%, by weight of the total weight of hydrocarbons in the composition. It will be appreciated that it is preferable to avoid perhalocarbons so as to minimise any greenhouse effect.
It has been found that the compositions of the present invention are highly compatible with the mineral oil lubricants which have been conventionally used with CFC refrigerants. Accordingly the compositions of the present invention can be used with mineral oil and alkyl benzene lubricants including naphthenic oils, paraffin oils and silicone oils, and there is no need to employ fully synthetic lubricants such as polyol esters (POE), polyalkyleneglycols (PAG) and polyoxypropylene glycols which are needed for many of the newer refrigerant compositions. Further details of suitable lubricants which can be employed are disclosed in EP-A-399817.